The present invention relates to demand type printing heads for ink-jet printing apparatus, and more particularly to an improvement wherein the printing nozzles associated therewith mounted closely together in the printing head.
Heretofore, several types of printing heads for ink-jet printing apparatus have been employed. One typical version is diagramatically illustrated in FIG. 1 wherein ink is supplied from a reservoir 1 by way of a conduit to a common ink-chamber 3 formed in a printing head 2. Ink flow channels 4 connect the common ink chamber 3 to a respective one of a plurality of nozzles 6 via pressure chambers each of which contains a piezoelectric-crystal element 5 driven by driving circuit 9. The channels 4 correspond to the elements of an image pattern.
In a printing operation, the piezoelectric-crystal elements 5 mounted in the pressure chambers are activated by electric signals which correspond to image pattern signals and ink is pressurized causing ink-droplets to be ejected through nozzles 6.
A feature of the above described demand type printing unit is that it does not require a system for recovering unused ink because ink is ejected only when necessary and in response to an image pattern signal so that ink consumption is minimized.
Furthermore, these demand printing devices enjoy excellent reliability and can be made relatively small and light weight, and correspondingly low in cost. Still further, a number of channels may easily be provided on a single printing head, so that high resolution and high speed printing may be carried out and color printing is possible.
In these prior art devices such as is illustrated in FIG. 1, the nozzles 6, ink flow channels 4, and pressure chambers containing the piezoelectric-crystal elements 5 generally all face the same direction as shown in FIG. 1. There have been many attempts to devise various mountings for multi-nozzles in a single head. One type employes ink flow channels and pressure chambers on both sides of a single printing head and provides up to 24 to 32 nozzles.
Problems arise, however, for the reason that it is difficult to mount a significantly larger number of nozzles on a single printing head of given size, because it would require smaller ink flow channels and pressure chambers, and even smaller nozzles.